email is blocked, then unblocked, blocked, unblocked, blocked ...

For the fourth time in the last month, I am being shut out of my comcast email with a 3rd party app - Thunderbird. I have been using Thunderbird for over 10 years, and it has worked well. I am using the pop3 settings and I am leaving the messages on the server. I also have use third-party apps selected in my comcast settings. I am currently traveling and using internet in Italy. About 3-4 weeks ago, I experienced a problem where Thunderbird reported:

"Sending of password for user [Edited: "Personal Information"] did not succeed. Mail server pop3.comcast.net responded: [AUTH] Your IP is on a blocklist, for more details please go to https://www.spamhaus.org/query/ip/XXX.XX.XXX.XX "

It then asks for me to input my password again. This happened for two straight days, and I then called Comcast Security Assurance, which was an utter waste of time. They didn't have an answer and connected me to technical service, which was perplexed also had no answers. They blamed Thunderbird, but it also happens when I try to use Outlook. It was a wasted hour of endless apologies and thankyous, but no solutions.

The above website says that this is no big deal, and it should all work if it is configured properly, which it is.

Then mysteriously, a day afterwards, it seemed to be resolved. Then, the problem returned. Only to be resolved again. Then it occurred again to be resolved for several weeks. Then again, this morning the same problem occurred. 

At the same time, I cannot access email on my Samsung phone. This first started while being connected to the Wifi on this network but persisted even when I switched to 5G.

I have no issue accessing email using Comcast's web portal. I prefer not to as it is slow and clunky and I need to have access to emails even when I am not connected.

This is getting to be frustrating beyond endurance as it is clearly an issue with Comcast, and this is becoming unreliable and unusable. 

Help! What is the solution and why does it keep recurring? And how do I keep it from happening again?